1. Field of the Invention
This invention relates to a method and apparatus for feeding items from a stack and more particularly to a method and apparatus for feeding items from the bottom of a stack.
2. Description of the Prior Art
Sheet feeders for feeding plain single sheets and folded sheets and envelopes are known. Generally the feeder devices can be classified as top-sheet feeders and bottom-sheet feeders. In a top-sheet feeder the uppermost or top sheet is removed from a stack by the feeder mechanism and serially conveyed to other devices. In a bottom-sheet feeder the lowermost sheet is removed from the stack by the feeder mechanism and conveyed serially to other devices.
Examples of feeders are disclosed in the following U.S. Pat. Nos. 1,385,468; 2,195,576; 1,127,796; 2,251,945 and 2,853,296. The first two patents relate to top-sheet feeder mechanisms where the uppermost sheet is removed from the stack. In U.S. Pat. No. 1,385,468 a cylinder is positioned above an endless conveyor and closely adjacent thereto. The stack of sheets abut the nip between the cylinder and the endless conveyor and the leading edge is suitably supported on a spring-loaded arm. The upper cylinder has a resilient insert that has a surface that conforms with the configuration of the cylinder surface. The resilient member frictionally engages the uppermost sheet and moves it into frictional engagement with the endless conveyor positioned therebelow. U.S. Pat. No. 2,195,576 discloses a similar top-sheet feeder where a pair of cylinders are positioned in substantially abutting relation with each other and adjacent to the stack. Again the leading edge of the stack is supported by a support member and the upper cylinder has a plurality of resilient inserts therein that frictionally engage the uppermost sheet and convey the uppermost sheet to the nip between the adjacent cylinders. An auxiliary feed device is provided to urge the trailing edge of the uppermost sheet toward the nip between the cylinders. The top-sheet feeder as disclosed in the above patents is unsuitable for feeding items having irregular thickness or filled envelopes. Further the top-sheet feeders disclosed are not suitable to feed mixed items of various thicknesses. Where more than one of the sheets is withdrawn from the stack, i.e., two of more sheets, the plurality of sheets are removed from the stack and are fed by the above-discussed feeders as a multiple of sheets causing jams in the mechanism to which the sheets are fed. Neither of the top-sheet feeders provide a means to feed only single sheets from the stack and to distinguish between a single and multiple sheets withdrawn from the stack.
The next three enumerated patents disclose bottom-sheet or item feeders. U.S. Pat. No. 1,127,796 discloses a feeder for envelopes which includes a segmented cylinder that engages the lowermost envelope and removes the lowermost envelope from the stack. U.S. Pat. No. 2,251,945 discloses a bottom-sheet feeder wherein the cylinder has a plurality of rows of vacuum ports that engage the bottom sheet and position the bottom sheet on an endless conveyor. U.S. Pat. No. 2,853,296 is similar to the last-named patent in that a plurality of vacuum ports are provided on a cylinder to engage the bottom sheet of the stack and convey the bottom sheet to another conveyor means. None of these references, however, provide apparatus that is suitable to feed mixed items of various thicknesses nor to distinguish between single and multiple items removed from the stack that are thereafter singly separated from each other and conveyed as single sheets or elements to a second conveyor.
There is a need for a feeder device that is capable of feeding items of various thicknesses and feeding only single items to another conveying device. There is also a need for a feeder device that prevents more than one item from being completely removed from the stack at the same time.